The present invention relates to a method of spraying particles, a method for producing a liquid crystal display device, a particle sprayer and a liquid crystal display device.
With the advancement of electronic technology, particles have been put to wide, practical use in various fields. Among such particles, there maybe mentioned particles used as spacers in liquid crystal display devices, for instance.
In one of the fields of application of such particles, liquid crystal display devices, for instance, are widely used in personal computers, portable electronic apparatus and the like. Generally, a liquid crystal display device comprises, as shown in FIG. 75, a liquid crystal layer 7 sandwiched between two paired insulating substrates 1, on which color filters 4, a black matrix 5, transparent electrodes 3, an alignment layer 9 and so on are formed.
The distance between the above paired insulating substrates 1, namely the thickness of the liquid crystal layer, influences the transmittance of light and, therefore, if the liquid crystal layer thickness is not maintained constant all over the display area of a liquid crystal display device, satisfactory display will not be attained. For this reason, spacers 8, for example glass fibers or truly spherical plastic beads, are disposed between the paired insulating substrates so that the liquid crystal layer thickness may be maintained constant all over the display area.
These spacers are dispersed uniformly on the alignment layer, for example, by spraying, together with a compressed gas, from a nozzle (dry spraying) or spraying of a liquid composed of spacers and a volatile liquid (wet spraying) after alignment layer formation. Thereafter, the insulating substrate is paired with a counterpart insulating substrate for panel alignment and a liquid crystal, for example a nematic liquid crystal, is filled into the space between the paired insulating substrates with spacers sandwiched therebetween.
When, however, spacers are disposed also on pixel electrodes within the display area, light leakage occurs from such spacers and the substantial aperture ratio is thereby reduced, so that such problems as display unevenness and reduced contrast arise.
For solving such problems as mentioned above, it is only necessary to dispose spacers only in those electrode gaps which are nondisplay areas, namely only at sites of a black matrix, which is constituted of a light shield layer. The black matrix is provided for the purpose of improving the display contrast of the liquid crystal display device and, in the case of TFT type liquid crystal display devices, for the purpose of preventing their elements from erroneously operating in response to external light.
For TFT type liquid crystal display devices, a technology of disposing spacers at sites corresponding to the black matrix, namely at sites other than display pixel sites, is disclosed in Japanese Kokai Publication Hei-04-256925 which comprises maintaining the gate electrode and drain electrode at the same electric potential in the step of spraying spacers. Further, Japanese Kokai Publication Hei-05-61052 discloses a method comprising applying a positive voltage to the circuit electrodes and charging spacers negatively and spraying them by dry method. In these technologies, it is intended to control spacer disposition by applying a voltage to electrodes formed on the substrate.
However, they have a problem. Namely, application of a voltage to the substrate having thin film transistors (TFTs) formed thereon, for the purpose of controlling the spacer disposition, may lead to destruction of elements by that voltage, hence to failure to function as a liquid crystal display device.
There is another problem. Namely, such technologies as mentioned above cannot be employed in STN (supertwisted nematic) type liquid display devices since the sites corresponding to the black matrix are spaces among transparent electrodes.
On the other hand, as a technology of disposing spacers in spaces between stripe-form transparent electrodes constituted by disposing a plurality of linear transparent electrodes in parallel on a substrate, as in STN type liquid crystal display devices, there are disclosed, in Japanese Kokai Publication Hei-03-293328 and Japanese Kokai Publication Hei-04-204417, methods of producing liquid crystal display devices which comprise charging spacers either positively or negatively and applying a voltage of the same polarity to the transparent electrodes on the substrate in the step of spacer spraying.
In particular, according to Japanese Kokai Publication Hei-04-204417, a conductor is disposed below the electrode substrate in a spacer sprayer for positive voltage application so that the velocity of falling of negatively charged spacers may be controlled. It is further disclosed that, for avoiding adhesion of negatively charged spacer particles to the wall of the spray chamber, the chamber should be made of a conductor to enable negative voltage application.
However, when, in practicing these methods, the spacer charge amount and/or the voltage to be applied to electrodes is selected at a low level (voltage value: not higher than about 1,000 V), the repulsive force (repellent force) between spacers and electrodes becomes weak, and the force for shifting spacers to interelectrode spaces becomes insufficient, hence the selectivity toward spacer disposition in electrode-free areas (interelectrode areas) becomes poor, with the result that a number of spacers are disposed also on each electrode, as shown in FIG. 76.
Conversely when the spacer charge amount and/or the voltage to be applied to electrodes is increased (voltage value: about several kilovolts), the repulsive force between spacers and electrodes becomes strong and the selectivity toward spacer disposition in electrode-free areas (interelectrode areas) is improved, as shown in FIG. 77.
In this case, however, the repulsive force acts more strongly over the set of electrodes, so that the tendency of spacers to be turned out of the domain of the electrodes increases; as a result, no spacers are disposed at all in the peripheral region of the electrode domain, hence the cell thickness cannot be controlled in the peripheral region of the electrode domain. Although such phenomenon occurs already at a state at which the repulsive force is still weak, the area of spacer-free portions unfavorably and markedly increases as the repulsive force increases.
In Japanese Kokai Publication Hei-08-76132, there is disclosed a method of disposing spacers more selectively as compared with the methods mentioned above. The method comprises charging spacers to be sprayed either positively or negatively, applying a voltage opposite in polarity of the spacer charge to first electrodes provided in areas on the insulating substrate where spacers are to be disposed, and applying a voltage of the same polarity as the spacer charge polarity to second electrodes provided in areas on the insulating substrate where no spacers are to be disposed, to thereby apply a repulsive force and an attractive force between spacers and the electrodes so that the spacers may be disposed either on the first electrodes or on the second electrodes with good selectivity.
This method, however, has a problem in that the contrast is decreased by the occurrence of spacers on the electrodes. Another problem is that when this method is applied to the production of simple matrix type liquid crystal display devices, it is necessary to form electrodes for spacer disposition in addition to the pixel electrodes and the aperture ratio decreases accordingly.
Accordingly, it is an object of the present invention to solve the above problems and provide a method of spraying particles by which predetermined quantities of particles can be disposed on specified electrodes, in particular a method of spraying particles by which spacers can be sprayed in interelectrode gaps selectively even in the case of substrates comprising pattern-forming transparent electrodes, such as those used in liquid crystal display devices, and a method of producing liquid crystal display devices of high contrast and high display uniformity by which spacers can be disposed in interelectrode gaps without sacrificing the aperture ratio and by which spacers can be disposed on the substrate without irregularity to attain a uniform cell thickness over the whole substrate, as well as a particle spraying apparatus and a liquid crystal display device.
In a first aspect, the present invention provides a method of spraying particles
which comprises applying a voltage of the same polarity as the particle charge polarity to a plurality of electrodes formed on a substrate
and spraying the particles while utilizing the repulsive force operating on the particles,
wherein means is employed for preventing the particles from being forced out of the electrode domain comprising the plurality of electrodes.
In a second aspect, the invention provides a method for producing a liquid crystal display device comprising
spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and having at least one display area and a second substrate to be disposed opposedly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein accessory electrodes are provided outside the display area
and, in spraying positively or negatively charged spacers onto the substrate, two or more voltages differing in voltage value are applied to respective transparent electrodes
and a voltage is applied to the accessory electrodes as well to thereby control the electric field generated above the transparent electrodes and above the accessory electrodes so as to cause selective spacer disposition only in a predetermined transparent electrode gap among the gaps between respective neighboring transparent electrodes.
In a third aspect, the invention provides a method for producing a liquid crystal display device comprising
spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and a dummy electrode and a second substrate to be disposed opposedly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, two or more voltages differing in voltage value are applied to respective transparent electrodes and a voltage is applied to the dummy electrode as well,
the predetermined transparent electrode gaps in which spacers are to be selectively disposed are provided between respective two neighboring transparent electrodes,
the number of transparent electrodes is even,
and the two or more voltages differing in value are applied in a manner such that when the spacer charge polarity is positive (+), the lowest of the two or more voltages differing in value is applied to the respective two neighboring transparent electrodes between which spacers are to be disposed in the middle,
and when the spacer charge polarity is negative (xe2x88x92), the highest of the two or more voltages differing in value is applied to the respective two neighboring transparent electrodes between which spacers are to be disposed in the middle.
In a fourth aspect, the invention provides a method for producing a liquid crystal display device comprising
spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and a dummy electrode and a second substrate to be disposed opposedly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposed in close contact with an earthed conductive stage,
a conductor is provided in a state electrically insulated from the conductive stage,
said conductor being a conductive frame having an opening,
and said conductive frame being disposed on the periphery of the substrate with or without partial overlapping with the substrate periphery,
and wherein a voltage is applied to the transparent electrodes and the conductive frame.
In a fifth aspect, the invention provides a method for producing a liquid crystal display device comprising
spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and an alignment layer and having at least one display area and a second substrate to be disposed opposedly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposed in close contact with an earthed conductive stage,
a voltage having the same polarity as the spacer charge polarity is applied to the transparent electrodes on the substrate,
a conductor is provided, outside the display area, in a state electrically isolated from the conductive stage
and a voltage having the same polarity as the polarity of the voltage applied to the transparent electrodes is applied to the conductor to thereby form almost the same electric field within and without the substrate.
In a sixth aspect, the invention provides a method for producing a liquid crystal display device comprising
spraying spacers onto at least one of a first substrate comprising at least pattern-forming transparent electrodes and an alignment layer and having one or more display areas and a second substrate to be disposed opposedly above the first substrate
and filling a liquid crystal into the space between both the substrates,
wherein, in spraying positively or negatively charged spacers onto the substrate, the substrate is disposed in close contact with an earthed conductive stage smaller in size than the substrate to allow the substrate periphery to be apart from the conductive stage
and a voltage of the same polarity as the spacer charge polarity is applied to the transparent electrodes on the substrate.
In a seventh aspect, the invention provides a particle sprayer for disposing charged particles selectively on a substrate having a plurality of electrodes
which comprises a nozzle for spraying charged particles onto the substrate,
a conductive stage having a fixed position and serving to hold the substrate onto which charged particles are to be sprayed,
a plurality of push-up pins for mounting the substrate on and dismounting the substrate from the conductive stage,
a probe for applying a voltage identical in polarity with the charged particles to a plurality of electrodes on the substrate disposed on the conductive stage,
and a conductor being electrically insulated from the conductive stage,
said conductor being a conductive frame provided with an opening smaller in size than the substrate,
and said conductive frame being disposed on the top of the substrate disposed on the conductive stage and being applied a voltage of the same polarity as the charged particle polarity thereto.
In an eighth aspect, the invention provides a liquid crystal display device as obtainable by utilizing the method of spraying particles according to the first aspect of the invention.
In a ninth aspect, the invention provides a liquid crystal display device as obtainable by the method for producing a liquid crystal display device according to the second or third aspect of the invention.
In a tenth aspect, the invention provides a liquid crystal display device as obtainable by the method for producing a liquid crystal display device according to the fourth, fifth or sixth aspect of the invention using the particle sprayer according to the seventh aspect of the invention.